Direct-on ceramic coating of carbon-rich iron

ABSTRACT

A process is disclosed for preparing an iron workpiece containing at least 0.03% by weight carbon for a direct-on, onefire ceramic or enamel coat. A substantially continuous layer of substantially pure iron is electrodeposited on a surface of the carbon-rich iron workpiece from a liquid medium containing iron ions while using the workpiece as a cathode. The polarity of the electrodeposition is then reversed to remove some of the iron deposited and produce an exposed, fissured, textured surface in the pure iron layer. When a ceramic coat is conventionally applied over the fissured surface, it adheres well, even though the iron workpiece may contain appreciable amounts of carbon which normally would prevent such adherence for a direct-on ceramic coat. Optionally, the cathodic deposition of iron may comprise a deposition of a non-porous layer followed by an overlay of porous iron and/or take place from an aqueous medium having an acidic pH. A film of a covering metal such as nickel may also be deposited over the fissured layer prior to depositing the ceramic coat.

United States Patent [191 Ruderer 1 Dec. 2, 1975 Clifford G. Ruderer, Brecksville, Ohio [75] Inventor:

[73] Assignee: Ferro Corporation, Cleveland, Ohio [22] Filed: Dec. 23, 1974 [21] Appl. No.: 535,441

[52] US. Cl. 204/35 R 204/37 R; 204/38 C [51] Int. CIR... C25D 5/12; C-25D 5/48; C25D 5/50 [58] Field of Search 204/38 C, 35 R, 37 R [56] References Cited UNITED STATES PATENTS 2,351,811 6/1944 Frank 204/38 C 2,639,264 5/1953 Chester 204/38 C X 3,773,629 11/1973 Sieckmann et al 204/38 C Primary Examiner'G. L. Kaplan Attorney, Agent, or Firm-Milton L. Simmons; Wesley B. Taylor [5 7] ABSTRACT A process is disclosed for preparing an iron workpiece containing at least 0.03% by weight carbon for a direct-on, one-fire ceramic or enamel coat. A substantially continuous layer of substantially pure iron is electrodeposited on a surface of the carbon-rich iron workpiece from a liquid medium containing iron ions while using the workpiece as a cathode. The polarity of the electrodeposition is then reversed to remove some of the iron deposited and produce an exposed, fissured, textured surface in the pure iron layer. When a ceramic coat is conventionally applied over the fissured surface, it adheres well, even though the iron workpiece may contain appreciable amounts of carbon which normally would prevent such adherence for a direct-on ceramic coat. Optionally, the cathodic deposition of iron may comprise a deposition of a nonporous layer followed by an overlay of porous iron and/or take place from an aqueous medium having an acidic pH. A film of a covering metal such as nickel may also be deposited over the fissured layer prior to depositing the ceramic coat.

22 Claims, N0 Drawings DIRECT-ON CERAMIC COATING OF CARBON-RICH IRON BACKGROUND OF THE INVENTION The preparation of the surface of steel or other ironcontaining workpiece to receive a coat of ceramic (often also called enamel-coat or porcelain enamel) has presented a number of problems to the industry if a tightly adherent, defect-free ceramic coat is to be obtained. Preparation of iron-containing workpiece for enameling presently involves a long and fairly complex series of operations performed in both hot and cold solutions which require careful control of temperature, pH, and concentration.

In one present practice, two ceramic coats are sequentially applied, the first being called a ground coat and the second, a cover coat. For each coat, it is necessary to use a special frit composition. Each frit composition is milled, dried, and after application to the metallic workpiece, each coat must in turn be fired.

In order to eliminate the ground coat application and all that it entails, so -called direct-on or a single application of an enamel or ceramic coat has been proposed. In this case, the application is limited to special and expensive grades of steel, such as zero carbon steel which may contain about 0.003 percent carbon. Further, it is necessary to etch the surface of such workpiece, as with sulfuric acid as a preliminary step which ordinarily is more extensive than for a ground coat and cover coat application. For example, the acid etch may remove as much as 3.5 grams per square foot of zero carbon which is relatively expensive.

Not only does a workpiece previously designed for direct-on enameling require a more severe etch, but it also generally requires a heavier deposit of nickel to obtain adherence in the absence of the use of highly colored adherence oxides, such as cobalt oxides, found in ground coats. Since the higher carbon contents of steel like cold rolled steel result in unacceptable enamel defects if ground coats are omitted, these grades of steel have not been successfully used for direct-on ceramic or enamel coating. If a direct-on ceramic coat isattempted on a carbon-rich steel substrate, such as cold rolled steel, the resulting ceramic coat not only has poor adherence but is subject to fish scaling and reboiling defects. Bubbles, pits or specks almost inevitably develop in the surface of a single ceramic coat applied to such a substrate, marring its uniformity and texture. The ceramic coat is also more prone to chipping.

The art has previously attempted to adapt carbonrich iron alloys for a direct-on or one-fire ceramic coat. In U.S. Pat. No. 2,819,207 to Shepard, for example, the disclosed important aspect of the process of that patent is said to be the provision of a finely divided coat of cobalt or nickel on a cleaned surface by means of an electrodeposition procedure. U.S. Pat. No. 3,078,180 to Zander et al. discloses a pickling and etching technique which includes closely controlled treatments of an enameling stock in solutions of ferric sulfate and sulfuric acid, so that scale and rust are effectively removed and a fine grained, uniformly etched metal surface is said to be obtained.

SUMMARY OF THE INVENTION The principal object of the present invention is to provide a process for preparing a carbon-rich, ironcontaining workpiece, such as cold rolled steel, for a direct-0n, one-fire ceramic coat operation in which the ceramic or enamel coat adheres well to the workpiece and is not subject to spalling, chipping, fish scaling, reboiling, and the like which have so often characterized other attempts to apply a direct-on ceramic coat to such carbon-rich substrates. A related object is to achieve adherence of a ceramic coat to an iron workpiece without conventional pickling or the use of hot solutions, or the use of adherence-promoting additives.

Prior attempts to enamel a carbon'rich iron workpiece have been directed to covering the iron surface with non-ferrous metals, such as nickel or cobalt. It has now been surprisingly found that iron itself can form a suitable barrier between the workpiece and a ceramic coat, if the iron is deposited in a substantially pure form and if the deposited iron layer is treated before applying the ceramic coat by electrolytically removing some of the iron to form a fissured surface.

In general, the process is carried out by electrodepositing a substantially continuous layer of substantially pure iron onto a carbon-rich iron workpiece, such as cold rolled steel, from a liquid medium containing iron ions while using the workpiece as a cathode. Preferably, the iron is electrodeposited in a two-step operation; first, as a non-porous, dense layer, and then as a porous layer. The polarity of the electrodeposit is next reversed to remove some of the deposited iron and produce an exposed, fissured surface in the substantially continuous iron layer. Thereafter, a ceramic coat is conventionally applied. Because the ceramic coat encounters only the layer of substantially pure iron, the ceramic-iron metal interface behaves as though the en tire workpiece were composed of pure iron or of very low carbon steel.

The simple step of depositing substantially pure iron on the workpiece replaces much of the prior preparation techniques, especially pickling and etching steps, which were usually performed at elevated temperatures. The present process therefore eliminates much of the work that was formerly undertaken to apply either a ground coat-cover coat application or a directon application of a ceramic coat.

Further improved results are obtained in the present invention if the electrolytic removal of some of the deposited iron is carried out in an acidic medium. The conjointremoval of iron and simultaneous etching action afforded by the acidic medium produce a more severely fissured surface which is even better adapted to receive a ceramic coat in a tight, adherent bond.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A representative series of steps of treatment for a workpiece, defining one form of the present process, includes:

1. Cleaning and degreasing.

2. Descaling.

3. Rinsing.

4. Electrodepositing substantially pure iron.

5. Increasing surface area of deposited iron by current reversal.

6. Rinsing at room temperature. 7. Applying flash coating of covering metal.

8. Rinsing at room temperature.

9. Drying.

10. Applying ceramic coat.

Only steps 4 and 5 are critical to the invention, and considerable variation is permissible in these steps as well as in the other non-critical steps. Considering these example steps in greater detail, steps 1 through3 are designed merely to clean the surface of the carbonrich workpiece. If the workpiece is already sufficiently clean to accept the electrodeposition, steps 1 through 3 can be eliminated. Normally, however, aworkpiece from stock contains oil, rust, scale, dirt, etc. spread over its surface.

The cleaning, degreasing, and descaling steps may be carried out singly or simultaneously by any suitable means including one or more of: washing with soap, aqueous solutions of alkaline agents such as alkali resinate or sodium orthosilicate, organic solvents, acid pickling, sand blasting, and anodic or cathodic cleaning and pickling in known, appropriate solutions. For example, in one cathodic pickling operation, the workpiece was treated with a 7% sulfuric acid aqueous solution at room temperatures (65F to 85F) for five minutes at a current density of 66 amperes per square foot. The descaling operation was similar to the degreasing operation except that the workpiece was used as the anode. Thereafter, the workpiece was rinsed with tap water at room temperatures.

The electrodeposition of step 4 is critical to the invention. In general, the electrodepositing forms a substantially continuous layer of substantially pure iron onto the carbon-rich iron workpiece from a liquid medium containing iron ions while using the workpiece as a cathode. The obtaining of a substantially pure iron deposit is realized by depositing metal from solution containing ions of the metal. The electroplating medium maybe any liquid adapted to transport iron ions under an electromotive force and may include organic liquids such as benzene, zylene, higher molecular weight alcohols such as ethylene glycol, propylene glycol, and the like. However, the preferred liquid medium is water because of its ready availability, lack of toxicity, and its ability to serve as a solvent for many ionizable iron compounds.

Any iron compound which furnishes ions in the liquid medium may be used. For example, ionizable, water soluble iron salts may be used as iron sulfate, iron chloride, iron acetate, iron bromide, iron carbonate, iron iodide, iron nitrate, mixtures thereof, and the like. A concentration of the iron compound in the electroplating medium is not critical, since the time of deposition need only be varied until a sufficient amount of the substantially pure iron is deposited. As a rule, the cathodic deposition of substantially pure iron continues until about 5 grams per square foot to about 20 grams per square foot has been deposited on the workpiece area. Similarly, the current density is not critical and may, for instance, be in the range of about 10 amperes per square foot to about 40 amperes per square foot for about 5 minutes to about 30 minutes.

As a modification providing improved results, the iron layer is preferably deposited as a two-step operation in which an initial, dense, non-porous layer is deposited, and a porous substantially pure iron layer is then deposited thereover, both being electrodeposited with the workpiece as a cathode. The reasons why a two-step operation offers improved results is not clearly known, but it is believed that the dense layer more effectively prevents migration of unwanted oxides, carbides, etc., through the iron layer to reach the subsequently applied ceramic coat with deleterious effects; while the outer porous layer has increased surface area which promotes better adhesion with a ceramic coat.

One technique that has been quite successfully used to vary the porosity of the deposited iron layer is varying the density of the electroplating current. Thus, a dense, non-porous layer is deposited at relatively low current densities; while a porous layer is deposited at relatively high current densities. As an example, a nonporous iron layer can be deposited at a current density of about 10 amperes per square foot to about 40 amperes per square foot, and a porous layer can be deposited at a higher current density of about 40 amperes per square foot to about 100 amperes per square foot. When a dual iron layer is used as just described, the dense, non-porous layer and the porous layer are each deposited at about two grams per square foot to about twelve grams per square foot of workpiece area. Thus, current density has a significant effect on the porosity and microstructure as well of the substantially pure iron electrodeposit. In general, the dense, non-porous layer is relatively equiaxed, while a relative increase in current density results in a more porous layer which has a columnar pattern of grain growth. Since an increase in the temperature of the electroplating bath permits deposition of dense, non-porous iron layers at relatively higher current densities as compared to the use of plating baths at lower temperatures, use of hot electroplating solutions are of some value in reducing the times required to achieve an iron layer of desired thickness. However, it is an advantage of the present invention that it is possible to obtain good, acceptable results with respect to adherence of a ceramic coating when the electroplating solution is used at room temperatures.

Regardless of whether one or two coats of substantially pure iron are deposited as described, it is necessary in order to obtain the results sought by the present invention to increase the surface area of the deposited iron layer by reversing the electroplating current, that is, by using the workpiece as an anode. As a rule, the reversal of current is atsuch current densities and for such times as to remove about 1 gram to about 10 grams per square foot of the substantially pure iron layer. The effect of current reversal is to promote formation of an exposed, fissured, roughened textured surface which is at least partly responsible for-the good adherence of an after-applied ceramic coat. It is believed that the increase in surface area of the iron layer encourages formationof appreciable quantities of ferric iron which subsequently develop during initial stages of firing an afterapplied ceramic coat. Other ferric compounds may also be formed at this time, such as hydroxides and sulfates. It is hypothesized that the presence of ferric iron helps to maintain the saturation of ferrous iron at the ceramic coat/metal interface needed for adherence by introducing a continuing supply of ferrous ions into the interface by a reaction with the workpiece as represented by the following:

2Fe (Ill) Fe-3Fe (n The electroplating solution may be hot (over F) during current reversal if desired, but it is an advantage of the present invention that good acceptable'results are possible even when the electroplating solution is used at room temperatures.

As a modification, improved results have been noted if during current reversal the electroplating solution has an acid pH, for example, a pH from about 2 to about 6. A pH of 2 to 3 is preferred. The pH of the bath may be adjusted by adding any suitable material which does not introduce undesirable materials into the bath. Examples of such materials are sulfuric acid for reducing the pH, and iron powder for raising the pH. The reason why an acid pH improves the results is not entirely clear, but it is postulated that the formation of the fissured, textured surface is further enhanced by combining the electrolytic removal of some of the iron layer with a simultaneous acid etch of the layer. However, an acid etch by itself does not provide the desired results. The anodic removal of iron from the substantially pure iron layer is essential to satisfactory adherence of an after-applied ceramic coat.

The electrodeposited iron layer obtained as above described (whether with one or two iron coats) serves two basic functions. First, the iron layer acts as a barrier between carbides and other reactive impurities in the underlying substrate of the workpiece and oxygen and oxidizing compounds present in the enamel which is later applied or in the atmosphere. In this manner, evolution of gaseous reaction products and defects in a ceramic coat normally produced thereby are prevented. Second, the porous, electrolytically roughened, outermost surface of the iron layer provides a large surface area per unit area of the substrate of the workpiece, thereby increasing the quantity of ferric-ironcontaining oxide formed during the initial stages of firing.

As a further modification designed to improve results, a relatively thin coat of a covering metal may be deposited over the substantially pure iron layer prior to applying a ceramic coat. The covering metal is not necessary to the invention and its usefullness in providing improved results becomes even less if a non-porous iron layer and porous overlay of another iron layer are used as previously described. Useful metals which may define the covering include nickel, cobalt, copper, and manganese. Nickel is preferred. The metal covering is relatively thin, resembling a flash coating, for example, up to about 0.3 gram per square foot and preferable about 0.03 gram to about 0.1 gram per square foot.

The metal covering may be applied to the iron layer in any convenient manner, preferably after water rinsing the workpiece following the step of increasing the surface area of the deposited iron layer. For example, the metal covering may be applied by a chemical replacement action (in accordance with the electromotive series) as from a hot nickel sulfate aqueous solution; or by reducing an unstable salt of the metal in an aqueous solution, for instance, a nickel-containing hypophosphite solution; or by electrodeposition as from an aqueous solution of a nickel salt, for example, a solution of nickel chloride or nickel sulfate. Electrolytic deposition is preferred. It is postulated that the covering metal further enhances formation of ferric oxide during subsequent firing to form a ceramic coat. Salts and particularly water soluble salts of the other disclosed metals, cobalt, copper, and manganese, can be similarly used.

After rinsing the workpiece following application of the covering metal, it may be suitably dried in any convenient manner, such as leaving it to dry in the open atmosphere, blowing warm air currents over the workpiece, heating it directly, and the like. The workpiece is 6 now ready for application of a ceramic coat which can be applied in a conventional manner and which can comprise any known frit composition for steel. For example, the following may be used:

Ingredient Weight Percent sio 40 to 50 B 0 10 m 20 Na O 5 to [0 0 5 :0 l0 TiO l5 to 25 P 0 0 to 5 F 0 to 5 The frit is directly applied to the substantially pure iron layer (or over the covering metal if one is used) such as from an aqueous slip, and then the workpiece is dried and fired, for example, at a temperature of about 1200F to about 1600F, to fuse the frit particles and form a single ceramic coat. The coat is uniform and contains no pits or other defects. The ceramic coat has good adherence to the underlying metal surface.

EXAMPLE 1 Working Example The following describes in detail one form of the present invention. A specimen of cold rolled steel plate was used containing 0.08% C, 0.35% Mn, 0.005% P, 0.025% S and the balance iron. The specimen measured 4 inches by 6 inches and had a thickness of about 0.03 inch. In place of the cold rolled steel, hot rolled, killed, semi-killed, rimmed steel and other less expensive, non-premium steels containing appreciable amounts of carbon in excess of at least 0.03% carbon could have been used.

The workpiece was cleaned and degreased electrolytically with an aqueous solution of 7% by weight sulfuric acid at room temperatures using the workpiece as a cathode. Electric current was applied at a density of 66 amperes per square foot for five minutes. For heavily soiled workpieces, this time may be extended as required. The workpiece was next descaled using the same solution as for the cleaning and degreasing step but with the current reversed so that the workpiece was the anode. Current flow was maintained at 66 amperes per square foot for five minutes, after which the workpiece was rinsed with water at room temperatures in the absence of any electric current.

In this example both a dense, non-porous layer of iron and a porous layer of iron were used to define the substantially pure iron layer. Initially, a dense continuous layer of the substantially pure iron was electrodeposited onto the workpiece from an aqueous solution maintained at room temperatures and containing 40 grams per liter of FeSO .7H O and grams per liter of NI-I Cl. The solution has a pH of 2 to 3. With the workpiece as a cathode, the electrodeposition was carried out at a current density of 18 amperes per square foot for 15 to 20 minutes.

An overlay of a porous layer of substantially pure iron was next electrodeposited over the dense layer, using the same electroplating solution as in the first electrodeposition. This second electrodeposition was performed at a current density of 66 amperes per square foot for five minutes also with the workpiece as a cathode. According to X-ray diffraction techniques, both the non-porous and the porous layers of iron were substantially pure iron.

The surface area of the exposed face of the porous iron layer was then increased by reversing the current TABLE A Useful Iron Plating Baths Compound Concentration, g/l Concentration of Ionic Species. g/l Example FeSO,.7H O Nl-LCl (NH,) SO Fe NH, C SO,-

180 Fecl AH O ll 10 Fe SO4)3.XI'I2O 52.7 32.8 63.8 94.5

120 (NH,) SO

The present invention replaces virtually the entire to remove some of the electrodeposited iron. This op eration was carried out using the same electroplating solution except that the workpiece was used as the anode. A current density of 36 amperes per square foot for two minutes was used.

After rinsing the workpiece with water at room temperatures in the absence of any electric current, a flash coating of nickel was electrodeposited over the porous iron layer using the workpiece as a cathode. The electroplating bath was maintained at room temperatures and comprised an aqueous solution of 75 grams per liter of NiCl and grams per liter of NH Cl. It has a pH of about 7. The current was applied at a density of 9 amperes per square foot for 30 seconds. After once more rinsing the workpiece with water at room temperatures in the absence of an electric current, the workpiece was dried to the touch by flowing warm air over the treated surface.

The workpiece was now ready for application of a ceramic coat. A frit composition within the range previously disclosed was conventionally applied over the treated workpiece surface from an aqueous slip. The workpiece was then heated to evaporate the water, and then fired at a temperature of about 1400F for about 3.5 minutes to about 4.5 minutes to fuse the frit and form a ceramic coat, after which the workpiece was removed from the furnace and allowed to cool.

Photomicrographs taken of the ceramically coated workpiece indicate that the ceramic coat directly contacts only the electrodeposited substantially pure iron layer and does not contact the original substrate of the workpiece. The photomicrographs clearly show the outer fissured or porous surface of the iron layer disposed away from the workpiece, the fissures being filled with iron oxide. During firing to form the ceramic coat, the fused frit reacted with and partially dissolved only the electrodeposit of substantially pure iron and treated the workpiece as though it were composed entirely of substantially pure iron.

EXAMPLES 2 THROUGH 11 Electrodeposition parameters, such as current density, deposition time, and other values as given in Example 1, may be controlled and varied to provide a consistent and reproducible surface for enameling by simple trial and error. Similarly, the electroplating solution is not critical to the invention as long as iron ions are available for electrodeposition. The electroplating bath used in Example 1 can itself be varied as illusrelatively complex and costly metal preparation procedures now used, such as hot pickling, hot acid etching, and rinsing steps with a single electroplating bath maintained at room temperatures. Because an enamel or ceramic coat touches only the substantially pure electrodeposit of iron and not the actual substrate of the workpiece, direct-on ceramic coating of low cost grades of steel such as cold rolled steel is practical. Savings are realized not only by the use of less expensive steel but by elimination as well of ground coat enamels.

Although the foregoing describes several embodiments of the present invention, it is understood that the invention may be practiced in still other forms within the scope of the following claims.

I claim:

1. In a process for the direct-on, ceramic coating of a carbon-rich, iron workpiece, the improvements prior to depositing the ceramic coat of:

a. electrodepositing a substantially continuous layer of substantially pure iron onto said carbon-rich iron workpiece from a liquid medium containing iron ions while using the workpiece as a cathode, and

b. then reversing the polarity of the electrodeposit to remove some of the deposited iron and produce an exposed, fissured surface in said substantially continuous layer.

2. The process of claim 1 including applying a film of a covering metal onto said fissured surface.

3. The process of claim 2 in which said covering metal is nickel.

4. The process of claim 2 in which said covering metal is selected from the group consisting of nickel, cobalt, copper, and manganese.

5. The process of claim 1 in which said iron workpiece contains at least 0.03% by weight of carbon.

6. The process of claim 1 in which said iron workpiece is cold rolled steel.

7. The process of claim 1 in which said liquid medium is an aqueous solution of a water-soluble, ionizable iron compound.

8. The process of claim 1 in which said liquid medium is an aqueous solution of a water-soluble, ionizable iron compound and has an acidic pH to provide a metal etch simultaneously with said metal removal.

9. The process of claim 1 in which step a electrodeposits substantially pure iron on said workpiece in an amount of about 5 grams per square foot to about 20 grams per square foot.

10. The process of claim 1 in which step b removes from said deposited layer an amount of about 1 gram per square foot to about 10 grams per square foot.

11. The process of claim 1 in which step a comprises first electrodepositing a non-porous layer of substantially pure iron, and then electrodepositing thereover a porous layer of substantially pure iron.

12. The process of claim 1 in which step a comprises first electrodepositing a non-porous layer of substantially pure iron at a current density of about 10 amperes per square foot to about 40 amperes per square foot, and then electrodepositing thereover a porous layer of substantially pure iron at a higher current density of about 40 amperes per square foot to about 100 amperes per square foot.

13. The process of claim 1 in which step a comprises first electrodepositing a substantially non-porous layer of substantially pure iron at a first current density, and then electrodepositing thereover a more porous layer of substantially pure iron at a second and higher current density.

14. The process for preparing an iron workpiece containing at least 0.03% by weight of carbon for a directon ceramic coating without the use of an intermediate ceramic ground coat, comprising:

a. electrodepositing onto said workpiece a dense, non-porous layer of substantially pure iron in an amount of about 2 grams per square foot to about 12 grams per square foot from an aqueous electroplating bath containing iron ions, while using the workpiece as a cathode,

b. electrodepositing over said dense layer a porous layer of substantially pure iron in an amount of about 2 grams per square foot to about 12 grams per square foot from an aqueous electroplating 10 bath containing iron ions, while using the workpiece as a cathode,

c. reversing the polarity of the electrodeposit to remove some of the deposited iron in an amount of about 1 gram per square foot to about 10 grams per square foot to produce an exposed fissured, textured surface in the continuous layer, and

d. then forming a ceramic coat on said fissured, textured surface.

15. The process of claim 14 including applying a film of a covering metal onto said fissured surface prior to forming a ceramic coat.

16. The process of claim 15 in which said covering metal is nickel.

17. The process of claim 15 in which said covering is selected from the group consisting of nickel, cobalt, copper, and manganese.

18. The process of claim 14 in which said iron workpiece is cold rolled steel.

19. The process of claim 14 in which the electrodeposition of step a is carried out at a current density of about 10 amperes per square foot to about 40 amperes per square foot, and the electrodeposition of step b is carried out at a higher current density of about 40 amperes per square foot to about amperes per square foot.

20. The process of claim 14 in which forming a ceramic coat comprises depositing a dispersion of ceramic particles on said surface and then firing to fuse the particles and fonn a ceramic coat.

21. The process of claim 14 in which said aqueous electroplating baths have a pH of about 2 to about 6.

22. The process of claim 14 in which the electrodeposition of step a is carried out at a first current density, and electrodeposition of step b is carried out at a second and higher current density. 

1. IN A PROCESS FOR THE DIRECT-ON, CERAMIC COATING OF A CARBON-RICH, IRON WORKPIECE, THE IMPROVEMENTS PRIOR TO DEPOSITING THE CERAMIC COAT OF: A. ELECTRODEPOSITING A SUBSTANTIALLY CONTINUOUS LAYER OF SUBSTANTIALLY PURE IRON ONTO SAID CARBON-RICH IRON WORKPIECE FROM A LIQUID MEDIUM CONTAINING IRON IONS WHILE USING THE WORKPIECE AS A CATHODE, AND B. THEN REVERSING THE POLARITY OF THE ELECTRODEPOSIT TO REMOVE SOME OF THE DEPOSITED IRON AND PRODUCE AN EXPOSED, FISSURED SURFACE IN SUBSTANTIALLY CONTINUOUS LAYER.
 2. The process of claim 1 including applying a film of a covering metal onto said fissured surface.
 3. The process of claim 2 in which said covering metal is nickel.
 4. The process of claim 2 in which said covering metal is selected from the group consisting of nickel, cobalt, copper, and manganese.
 5. The process of claim 1 in which said iron workpiece contains at least 0.03% by weight of carbon.
 6. The process of claim 1 in which said iron workpiece is cold rolled steel.
 7. The process of claim 1 in which said liquid medium is an aqueous solution of a water-soluBle, ionizable iron compound.
 8. The process of claim 1 in which said liquid medium is an aqueous solution of a water-soluble, ionizable iron compound and has an acidic pH to provide a metal etch simultaneously with said metal removal.
 9. The process of claim 1 in which step a electrodeposits substantially pure iron on said workpiece in an amount of about 5 grams per square foot to about 20 grams per square foot.
 10. The process of claim 1 in which step b removes from said deposited layer an amount of about 1 gram per square foot to about 10 grams per square foot.
 11. The process of claim 1 in which step a comprises first electrodepositing a non-porous layer of substantially pure iron, and then electrodepositing thereover a porous layer of substantially pure iron.
 12. The process of claim 1 in which step a comprises first electrodepositing a non-porous layer of substantially pure iron at a current density of about 10 amperes per square foot to about 40 amperes per square foot, and then electrodepositing thereover a porous layer of substantially pure iron at a higher current density of about 40 amperes per square foot to about 100 amperes per square foot.
 13. The process of claim 1 in which step a comprises first electrodepositing a substantially non-porous layer of substantially pure iron at a first current density, and then electrodepositing thereover a more porous layer of substantially pure iron at a second and higher current density.
 14. THE PROCESS FOR PREPARING AN IRON WORKPIECE CONTAINING AT LEAST 0.03% BY WEIGHT OF CARBON FOR A DIRECT-ON CERAMIC COATING WITHOUT THE USE OF AN INTERMEDIATE CERAMIC GROUND COAT, COMPRISING: A. ELECTRODEPOSITING ONTO SAID SAID WORKPIECE A DENSE, NON-POROUS LAYER OF SUBSTANTIALLY PURE IRON IN AN AMOUNT OF ABOUT 2 GRAMS PER SQUARE FOOT TO ABOUT 12 GRAMS PER SQUARE FOOT FROM AN AQUEOUS ELECTROPLATING BATH CONTAINING IRON IONS, WHILE USING THE WORKPIECE AS A CATHODE, B. ELECTRODEPOSITING OVER SAID DENSE LAYER A POROUS LAYER OF SUBSTANTIALLY PURE IRON IN AN AMOUNT OF ABOUT 2 GRAMS PER SQUARE FOOT TO ABOUT 12 GRAMS PER SQUARE FOOT FROM AN AQUEOUS ELECTROPLATING BATH CONTAINING IRON IONS, WHILE USING THE WORKPIECE AS A CATHODE, C. REVERSING THE POLARITY OF THE ELECTRODEPOSIT TO REMOVE SOME OF THE DEPOSITED IRON IN AN AMOUNT OF ABOUT 1 GRAM PER SQUARE FOOT TO ABOUT 10 GRAMS PER SQUARE FOOT TO PRODUCE AN EXPOSED FISSURED, TEXTURED SURFACE IN THE CONTINUOUS LAYER, AND D. THEN FORMING A CERAMIC COAT ON SAID FISSURED, TEXTURED SURFACE.
 15. The process of claim 14 including applying a film of a covering metal onto said fissured surface prior to forming a ceramic coat.
 16. The process of claim 15 in which said covering metal is nickel.
 17. The process of claim 15 in which said covering is selected from the group consisting of nickel, cobalt, copper, and manganese.
 18. The process of claim 14 in which said iron workpiece is cold rolled steel.
 19. The process of claim 14 in which the electrodeposition of step a is carried out at a current density of about 10 amperes per square foot to about 40 amperes per square foot, and the electrodeposition of step b is carried out at a higher current density of about 40 amperes per square foot to about 100 amperes per square foot.
 20. The process of claim 14 in which forming a ceramic coat comprises depositing a dispersion of ceramic particles on said surface and then firing to fuse the particles and form a ceramic coat.
 21. The process of claim 14 in which said aqueous electroplating baths have a pH of about 2 to about
 6. 22. The process of claim 14 in which the electrodeposition of step a is carried out at a first current density, and electrodeposition of step b is carried out at a second and higher current density. 